In manual shift transmissions with a central gearshift lever shaft various components in the transmission are involved in producing selection and shifting forces. In particular, these components serve to assist the driver of the vehicle to move the gearshift lever in the shift gates in accordance with the gearshift diagram and at the same time, by virtue of this support, to avoid any damage to transmission components. The vehicle's driver should be able to sense which shift gate he is currently in with the gearshift lever. In this, particular attention should be paid to the transition into shift gates in which particularly low transmission ratios are engaged or in which the ratio for the reverse gear is engaged. If too low a transmission ratio or the reverse gear were to be engaged without the conditions of the vehicle being appropriate for this, especially because the speed is too low or a driving direction reversal is initiated without the vehicle first having come to rest, then the shifting devices and in particular the synchronization devices could be damaged. Also, by virtue of their structure frictional losses occur during the interaction of individual components, which in unfavorable cases can lead to a reduction of driving comfort.
To avoid undesired shift processes it must be possible to prevent the mechanical shift process by impeding the movement of the gearshift lever or at least making it more difficult. For example, a shift into a reverse gear should not be allowed if the vehicle is moving in the forward direction at more than an acceptable speed. To ensure this, barriers or stops are provided in the shifting device, which cannot be overcome or only so with substantial difficulty if the driver of the vehicle tries to move to the shift position in the gearshift diagram of the vehicle which contains the reverse gear.
From automotive technology gearshift actuating devices for selecting a shift gate and engaging a gear step in a transmission, in particular a manual change-speed transmission, are well enough known. To select a desired shift gate the driver can actuate a gearshift lever which can be coupled to a gearshift shaft by a gearshift linkage. By moving the gearshift shaft longitudinally the desired shift gate can be selected and by corresponding rotational movement of the gearshift shaft a gear can be engaged in the shift gate selected. In addition a shifting link is provided, which suitably translates the longitudinal and rotational movements of the gearshift shaft and guides the gearshift rails and shift operating means so as to engage a desired gear.
A shift locking device known from automotive technology comprises a spring-loaded locking pin with securing means. With this solution it can happen that when shifting into reverse, the shift gate containing the reverse gear is selected erroneously and an attempt is made to engage it, with resulting clashing noises from the clutch teeth. For example particularly hard locking means can be used to secure against slipping out of the reverse gear, but this makes it more difficult to engage the reverse gear even when this shift is desired.
DE 199 60 194 A1 discloses a device for producing restoring forces or higher selection forces on a gearshift shaft. The device comprises a guiding element, a pre-stress element, a stop, an abutment plate and at least three spring elements. By means of the spring elements different selection forces or different restoring forces can be produced for different selector positions. However, such a device correspondingly increases the structural fitting space needed in the axial direction of the gearshift shaft. Furthermore the device consists of numerous individual parts some of which are quite expensive and complicated to produce, since for example the guiding element must have corresponding guide-tracks.
From DE 102 51 351 A1 a shifting device is known, which comprises a gearshift shaft, a stop abutment for movement of the gearshift shaft in a shift gate with a reverse gear step, and an indicator device for the reverse gear position of the gearshift shaft. A locking element is provided, which enables both the stop and the actuation of the indicator device. The locking element comprises a tappet-rod and a spring element that acts on the tappet-rod. The locking device is arranged so that the tappet-rod engages in a recess of the gearshift shaft. The tappet-rod and the recess of the gearshift shaft have inclined faces that correspond with one another. When the inclined face of the gearshift shaft comes in contact with the inclined face of the tappet-rod, the stop for movement of the gearshift shaft in the shift gate with the reverse gear is produced.
For selecting the shift gate with the reverse gear two types of shift operation are distinguished, namely static and dynamic selection.
In static selection of the shift gate with the reverse gear, the inclined face of the gearshift shaft recess is already in contact with the inclined face of the tappet-rod before the shift gate with the reverse gear is selected. By means of the gearshift lever the driver of the vehicle exerts a force on the gearshift shaft, whereby the static friction between the tappet-rod and the gearshift shaft is overcome and the gearshift shaft moves in the direction of the shift gate with the reverse gear. During this the tappet-rod is pushed against the spring element of the locking device. Thus, in static selection of the shift gate with the reverse gear large friction forces (static friction) are active and a large selection force is therefore needed.
In dynamic selection of the shift gate with the reverse gear the inclined face of the gearshift shaft recess is not yet in contact with the inclined face of the tappet-rod before the shift gate with the reverse gear has been selected. By means of the gearshift lever the driver of the vehicle exerts a force on the gearshift shaft, moving it in the direction of the shift gate with the reverse gear. During this, the inclined face of the gearshift shaft recess encounters the inclined face of the tappet-rod while in motion, and the tappet-rod is pushed against the spring element of the locking device. But when the inclined faces of the gearshift shaft recess and the tappet-rod come in contact while in motion, the force required to overcome the stop effect is much smaller because the sliding friction between the gearshift shaft and the tappet-rod is substantially less than the static friction during static selection of the shift gate with the reverse gear. Thus, dynamic selection of the shift gate with the reverse gear requires a much smaller selection force than static selection of the shift gate with the reverse gear.
A disadvantage of such a device is that the difference between the selection forces needed for static and for dynamic selection of the shift gate with the reverse gear is fairly large, and this has an adverse effect on selection comfort.